The invention relates to a direct current arc furnace or direct current resistance smelting furnace It also relates to a hearth electrode for insertion into the hearth wall of a furnace and an electrode block having such a hearth electrode. Finally the invention also concerns a method of operating such a furnace.
DE-A1-31 06 741 discloses a contact electrode arrangement for electric arc or resistance smelting furnaces, having a base plate which is arranged outside the furnace brick lining structure and to which the outer ends of a plurality of bar-shaped electrodes are conductively connected, wherein the remaining part of the electrode extends into the furnace brick lining structure and is in contact with the molten bath in the furnace hearth. The base plate is disposed at a spacing beneath the furnace bottom. Provided between the base plate and the furnace bottom is an intermediate space into which can flow a fluid for cooling the electrode neck portions, the outside of the furnace and the base plate.
EP-B1-0 219 650 discloses a similar contact electrode arrangement which is in the form of an inter! changeable structural unit.
EP-A1-0 12 4 490 discloses a bottom electrode for a direct current arc furnace, which in the form of an electrically conducting prefabricated structural unit is connected to the metal bath and which rests by way of a layer of electrically conductive granular material on a connecting plate which has a downwardly extending fluid-cooled projection. The interchangeable electrically conducting structural unit which is in contact with the molten bath includes a plurality of metal bars, as current conductors. Also disposed therein are one or more porous bodies for the introduction of a gas, the function of which is to prevent overheating phenomena, by virtue of an increased bath movement. In addition, the structural unit is cooled by the gas which is passed through the porous bricks.
The object of the present invention is to improve the cooling of the electrodes in a direct current are furnace or resistance smelting furnace in order thereby to be able to increase the current loading of the electrodes and thus the output and capacity of the furnace. The invention also seeks to provide an electrode for a direct current arc furnace which permits an improvement in the firing conditions and stabilisation of the arc plasma. The invention also seeks to provide that, after the formation of a molten bath, bath movement for better distribution of the heat in the bath and a desired metallurgical treatment can be carried out with the cooling fluid for cooling the electrodes.
Finally, an object of the invention is to provide a hearth electrode which is distinguished by an increased cooling action and thus a higher current load-carrying capability.
In addition the invention seeks to provide an electrode block having such a hearth electrode, which block can be fitted into the hearth wall of a smelting furnace.
Finally, the invention seeks to provide a method of operating a furnace of the specified kind, which improves firing of the arc in the initial phase of the smelting procedure and promotes the formation of a stable arc plasma for rapid melting of the solid charge.